Method in the manufacture of fiber board



Feb. 27, 1968 A. J. A. ASPLUND 3,371,137

METHOD IN THE MANUFACTURE OF FIBER BOARD Filed April 21, 1965 m a N m 81 a; h N LO 05G):

ca LO ARNE JOHAN ARTHUR ASPLUND, Inventor BY ERIC Y. muson, Attorney 3,371,137 Patented Feb. 27, 1968 3,371,137 METHOD [N THE MANUFACTURE OF FIBER BOARD Arne Johan Arthur Asplund, Litlingo, Sweden, assignor to Defibrator Aktieholag, Stockholm, Sweden, a corporation of Sweden Filed Apr. 21, 1965, Ser. No. 449,775 Claims priority, application Sweden, Apr. 24, 1964, 5,132/ 64 3 Claims. (Cl. 264-121) ABSTRACT OF THE DISCLOSURE The method of making a fiber board comprising defibrating and/or grinding moist, steam-treated fiber pulp and delivering the pulp into and through an expansion nozzle into a chamber of lower pressure, wherein the pulp discharged as a jet into the chamber is given, under the expansion of the steam, a speed component in the direction of discharge and while it is dispersed about in the air space in the chamber in a manner to cause the fibers to be evenly distributed. After said expansion in the chamher, the fibers float down to the bottom of the chamber where they collect in a layer upon a traveling screen wire belt. The layer thus collected is then compressed and may be otherwise treated to produce the desired fiber board.

Background of the invention According to one method, the so-called wet method, the fiber pulp is then mixed with water and, if desired, chemicals of different kind such as sizing and/or binding chemicals, for improvement of the properties of the final product. The pulp suspension which is given a concentration of, for example, 1% fibers, is allowed to flow out onto a draining screen wire belt in a so-called pulp vat machine or wet press machine whereby a coherent pulp web is formed which is cut to appropriately dimensioned sheets. These are pressed to board units under high pressure and high temperature.

By the heating and defibration of the vegetable matter several substances-carbohydrates, lignin and other-are set free which are to be traced in the waste water from the plant when the above-mentioned wet method is applied. These substances which are set free as small fibers, the so-called nought fibers, and certain fiber fragments which also are contained in the waste water, can cause important difliculties through their contaminating effect if the waste water is allowed to flow into a water course or into similar natural water bodies.

Another method for production of wood fiber board consists mainly in drying of the fibers after their defibration and possible further brinding, to approximately complete dryness and in connection therewith or already in the defibration step, supplying some sizing substances such as synthetic resins or the like. The dried fiber pulp is then formed into sheets which in approximately the same manner as in the wet method mentioned hereinbefore are compressed under high pressure and at high temperature. The advantage with this so-called dry sheet forming is mainly that the board can be made smooth on both faces, that no water must be evaporated during the pressing step and that no contaminated waste water is to be developed. A drawback of this dry method is the relatively great consumption of synthetic resins to provide to the board units desirable strength properties. This influences the economical side of the manufacture since the synthetic resins are relatively expensive.

Summary of the invention One main object of the present invention is to provide a method which in general terms is free from the disadvantages of the two methods contemplated above but has their advantages. The principle is that after defibration and/or grinding of the vegetable material, the moist fiber pulp while being in a steam atmosphere at a temperature exceeding 108 C. is brought to expand in an expansion jet to a lower pressure, and, if desired, atmospheric pressure. As a result the fiber pulp discharged from the expansion nozzle is given, under action of the expansion of the steam, a speed component in the direction of discharge and is dispersed into the air space in a blow chamber whereby the fibers are evenly distributed.

The fiber discharged from the expansion nozzle, which preferably is adjustable, is very porous and free from clods. After the expansion, the fibers float down like snow in the blow chamber where they are collected in a layer on the said screen wire belt traveling over the bottom of said chamber. Said layer is then compressed or otherwise treated further according to known processes.

In connection with the expansion, preheated fresh air may be supplied to the blow chamber through one or a plurality of nozzles, if desired.

According to the method of the invention fiber board units can be produced which, in general, possess the most favorable properties of the wet-formed fiber board units by not requiring addition of expensive synthetic resins or similar substances for the sizing. By the absence of waste water the problem of contaminating natural water bodies is avoided and at the same time the yield becomes greater because the main part of the released substances remains in the fiber board units. Disregarded in this connection are several products of decomposition such as carbon dioxide, acetic acid or like compositions which escape together with the steam during the expansion step, the sheet forming step or the pressure step.

Description of the drawing Further objects and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawing which forms part of this specification and which in its single figure shows in a partly sectioned side elevation an apparatus for carrying out the method of the invention.

Description 0' the preferred embodiment Referring to the drawing, reference numeral 10 denotes a band conveyor which supplies raw material such as wood chips to a receptacle 11 formed with an opening at the bottom, into a hopper 12. Through a feeder device 13 the chips are advanced into a container 14 in which a preheating of the chips is elfected by means of steam which is supplied through a conduit 15 in which superatmospheric pressure may prevail. By means of a conveyor 16 the chip material is then fed into a defibrator 19 which is driven by a motor 17 and in which the chips are subjected to disintegration and grinding. The fiber may thereafter be fed through a conduit 20 to a second defibrator 21 Which is driven by a motor 22 for further disintegration or grinding in a manner known per se. The treatment of the wood chips in the apparatus 19 and 21 is effected at high temperature and under high pressurefor example at C. and 10 atmospheres pressurein contact with water and saturated steam. The apparatus 19 and 21 may both be of the disc type disclosed for example in Patent No. 2,891,733.

The fiber pulp is thereupon conducted through a pipe 25 to a web forming station consisting of a receptacle or biow chamber 29. In an adjustable expansion nozzle 27 which suitably discharges into an upper projecting portion 31 of the chamber 29, accompanying water or steam is brought to expand to the pressure prevailing in the chamber, which means atmospheric pressure, whereby the fibers are disconnected from one another and form a fiber dispersion in steam or gas atmosphere. The lower part of the chamber 29 is traversed by the upper part of an endless travelling screen wire belt 33 which is positioned on and around guide rollers 34, 36 and which by a driving device, not shown, is advanced through the chamber in the direction indicated by the arrow 35. Positioned below the underside of the upper part of the endless screen wire belt is a suction box 39 which through pipes 41 is in connection with the suction side of a fan 43. Fresh air taken in by a fan 49 passes through a pipe 51 to a heat exchanger 47 and therefrom through a pipe 53 to a heating device or heater S whereupon it is blown into the chamber 29 through one or more nozzles 59. The pressure side of the fan 43 discharges through a conduit 45 which is in connection with the heat exchanger 47 and thence with the surrounding atmospheric air through a pipe 48. Within the heat exchanger 47 a heat exchange is effected between the warm air escaping from the suction box 39 and the fresh air fed in through the fan 49, said fresh air, if desired, being heated still more in the heating device 55.

The dimensions of the chamber 29 are chosen so that the fibers discharged through the expansion nozzle 27 are distributed over the chamber in the cross and longitudinal directions thereof while floating separately down towards the screen wire belt 33 in the same manner as snowflakes, :1 sheeting of fibers being formed on said screen wire belt which increases in height in the direction of advance of the screen wire belt as will be seen from the figure. The water content of the fiber pulp fed through the conduit 25 is not so high as to cause free water particles to be flung into the chamber 29 through the nozzle 27. The fresh air blown in through the nozzle or nozzles 59 is adjusted as to its quantity and temperature so that the moisture content in the chamber 29 is kept below the level of saturation so as to avoid precipitation of condensate. The hot air supplied is thus not intended to bring about any drying effect proper on the fibers during their floating down in the steam and air atmosphere present in the chamber. An adjustment of the moisture content of the fibers to any desired uniform level can nevertheless be obtained by variation of the quantity, humidity, and temperature of the admitted air.

After the fiber sheeting on the screen wire belt 33 has left the chamber, the thickness thereof is equalized to a desired value by means of a stripper 61. Excess pulp is sucked up by a fan 63 and is conveyed through a tube 65 and a centrifugal type cleaner 67 back into the chamber 29. The outlet of said cleaner 67 may be located just in front of, and slightly above, the expansion nozzle 27 so that the returning pulp is met by the steam stream dis charged from said nozzle. The fiber sheeting thus stripped to a uniform thickness on the screen Wire belt 33 is compressed in a pressing device 69 and then in a known manner cut to individual sheet units.

The sheet unit is thereupon in known manner subjected to a pressing operation at increased temperature, the water content in the fiber pulp due to the pretreatment described above being so low that water in liquid state will not be pressed out other than perhaps to a very limited extent. The water quantity remaining with the fibers and which has not escaped in the state of steam, is, however, sufficiently great to ensure an interconnection of the fibers, but it may be assisted by a small addition of a binder if desired. The final hot pressing may be done in hydraulic or similar presses (not shown) under a pressure of a magnitude from 0.5 to 150 kilograms per square centimeter depending on the desired density of the produced board units.

The moist air escapes from the chamber 29 through the suction box 39. The heat content of this air is utilized for the preheating 0f the fresh air in the heat exchanger 47. The negative pressure produced in the suction box 39 assists in forming a fiber sheeting with a homogenous structure on the upper part of the screen wire belt 33. The heater may operate with steam as heating fluid or be equipped with an oil burner.

It the quantity of water which is to be evaporated in the hot press amounts to the same quantity as corresponds to the weight of the ready fiber boards, such boards cannot be manufactured with a smooth face on both sides, since the water quantity must escape from the board surface during the pressing operation. By applying pressing plates, formed with slots or holes, on one side of the sheet, it is, however, possible to produce boards sub stantially smooth on both surfaces and it is at least possible to avoid pattern marks of the screen Wire belt, otherwise so markedly distinguishable on available fiber boards.

As far as it becomes necessary in connection with the forming of board sheets from fibers originating from some vegetable material, sizing and/or binding materials can be introduced by suitable means either in connection with the defibration and/or grinding of the vegetable material or in the conduit 25, as by supply means 70 via conduit 71, or they can be spread into the chamber 29 in connection with the injection of air and the mixture of fibers, water and steam. This addition is, however, always substantially less than that which is required in the dry sheet forming method set forth above.

While one more or less specific embodiment of the invention has been shown and described, it is to be understood that this is for purpose of illustration only, and that the invention is not to be limited thereby, but its scope is to be determined by the appended claims.

I claim:

1. The method of manufacturing fiber board from cellulose material Which has been disintegrated into a fiber pulp comprising:

(21) causing a mixture of moist fiber pulp and steam under superatmospheric pressure and at an elevated temperature to expand through an expansion nozzle to a lower pressure whereby the fiber pulp is accelerated to a relatively high velocity and is spread upon emerging from the nozzle within an air space in a chamber;

(b) establishing a condition of moisture content of the fiber pulp introduced into the chamber at such a level that a collection of a layer of the fibers on a traveling belt is prevented from yielding any appreciable quantity of water in liquid state under a subsequent pressing operation, but that the quantity of water remaining with the fibers is sufficient to cause an interconnection of the fibers;

(c) said condition being established by controlling at least one of the relative factors of natural moisture content of the fibers, added moisture of superheated steam, and the addition of a drying gas to said chamber;

(d) collecting the fibers on said traveling belt at the bottom of the chamber; and

(e) pressing the fibers into fiber board.

2. A method as set forth in claim 1, wherein a limited quantity of a binding agent is added to the fibers prior to collection on said traveling belt.

3. A method as set forth in claim 1, wherein said drying gas consists of air of a lower moisture content than the air in said chamber.

References Cited UNITED STATES PATENTS 2,516,847 8/1950 Boehm 162-21 2,646,381 7/1953 Duvall 264-121 2,889,242 6/1959 Teichmann l622l ROBERT F. WHITE, Primary Examiner.

I. R. HALL, Assistant Examiner, 

